The present invention relates to a method for manufacturing an image pickup tube target using a Se-As-Te amorphous semiconductor having a heterojunction.
In the past, an image pickup tube target using a photoconductive film has used Sb.sub.2 S.sub.3 or PbO. Recently, there has been proposed a photoconductive target using Se-As-Te material which has an excellent spectral sensitivity characteristic and an excellent resolution and still has low lag characteristic and good dark current characteristic.
Since the Se-As-Te material has a very high resistivity, electron charges may be stored. In order to prevent such a phenomenon to improve a scanning characteristic of an electronic beam, it has been proposed to deposit a porous Sb.sub.2 S.sub.3 film on the Se-As-Te photoconductor film on the side of an electron gun. However, as shown in Japanese Laid-Open Patent Application 52-26192, when the porosity of the Sb.sub.2 S.sub.3 film is too low, cracks may occur in the film because of a difference between coefficients of thermal expansion of the Sb.sub.2 S.sub.3 film and the Se-As-Te film as the contrast of the video image is reversed by high velocity scanning, and when the porosity of the Sb.sub.2 S.sub.3 film is too high, the scanning characteristic of the electron beam is materially deteriorated and the decay lag time or build up lag time increases, or the lag characteristic (%) after 50 msec increases.